Women with cancer are significantly more likely to fall than other women and this puts them at higher risk of fall-related fractures, other injuries and disability. Our understanding of falls in women with cancer is relatively new. Currently, there are no evidence-based fall prevention strategies that specifically target female cancer survivors. The purpose of the proposed study is to compare the efficacy of two very distinct types of exercise, tai chi versus strength training, to prevent falls in women who have completed treatment for cancer. We propose a three-group, single-blind, parallel design, randomized controlled trial in women, aged 50-75 years old, who have completed chemotherapy for cancer comparing 1) tai chi to 2) strength training against 3) a placebo control group of seated stretching exercise. Women will participate in supervised study programs three times per week for six months and will be followed for an additional six months after formal training stops. The specific aims of this study are to: 1) Determine and compare the efficacy of both tai chi training and strength training to reduce falls in older female cancer survivors, 2) Determine the mechanism(s) by which tai chi and strength training each reduces falls and, 3) Determine whether or not the benefits of each intervention last after structured training stops. The proposed study is innovative in its approach because it is the very first attempt at a direct comparison of two prominent exercise modalities (e.g., tai chi and strength training), each with distinct training properties, to reduce falls in a population of cancer survivors. This innovation will lead to a better understanding of potential mechanisms that underlie improvements in balance and strength and subsequently, reduced falls in women with cancer. This innovation may also impact clinical practice in terms of choosing most effective rehabilitative methods for treating cancer patients with an elevated risk of falling. The long-term goal of the proposed research is to develop effective and practical interventions that target the specific health needs of cancer survivors. This application addresses the National Cancer Institute's strategic goals to invest in intervention research on long-term health in cancer survivors and the Institute of Medicine recommendations to broaden cancer care to prevent dysfunction and disability in the growing population of cancer survivors. This study is relevant to public health because there are over 6 million women who have survived cancer but who are at great risk of falling. Currently, evidence-based therapeutic treatment options specific to fall prevention in women with cancer are not available in the cancer rehabilitation field. The proposed study, therefore, addresses both an important public health problem and a critical barrier in clinical practice. If the aims are successfully achieved, findings from this study will not only generate new knowledge about the effectiveness of two exercise-based treatment options but will also advance clinical rehabilitative practice. These factors, combined with the fact that the two exercise regimens are easily accessible and implementable in practice, increase the potential impact of this research on the quality of life in women with cancer.